The present invention relates to a stereotactic radiosurgery method and a stereotactic radiosurgery apparatus for collectively projecting radiation (containing X-rays and gamma rays etc.) to a lesion of a patient for therapy.
One conventional stereotactic radiosurgery apparatus has been described in WO 89/05171. In this prior art apparatus, the X-ray beams are collimated by the stereotactic collimator mounted on the tip portion of the gantry, the treatment couch is rotated around the vertical axis, whereas the gantry is rotated around the horizontal axis, whereby the X-ray beams are projected to the lesion at various angles within the wide range. As a result, absorbed dose of a normal tissue (namely, no diseased tissue) located around the lesion is considerably lowered, as compared with absorbed dose of this lesion. Since the stereotactic radiosurgery apparatus owns such a feature, if the lesion would be located at the radiation projection position at high precision, effective therapy effects could be achieved. However, if the lesion would be positionally shifted from this radiation projection position, great damage would be given to the normal tissue of the patient. As a consequence, a position of the lesion of a patient must be positionally and continuously coincident with a radiation position at very high precision in the stereotactic radiosurgery method.
The method for positionally making the position of the lesion coincident with the radiation position will now be explained. First, a diagnosing apparatus (CT, MRI, simulator etc.) is employed to relatively calculate the position of the lesion with regard to such a base as a patient fixing member and a mark indicated on a skin of the patient. Subsequently, the patient is transported to a treatment couch, so that a basic point is positionally coincident with a radiation point. Finally, the treatment is moved only by a distance corresponding to a shift between the lesion and the basic point.
Alternatively, a lineacgraphy is employed to determine the radiation position. A "lineacgraphy" implies radioscopy with employment of radiation from a therapy accelerator. At this time, even when a radiographic image is acquired by utilizing such a narrow X-ray beam used in the stereotactic radiosurgery, it cannot be recognized to which portion of the patient, such a narrow X-ray beam is projected. To judge an anatomical position of the lesion, the stereotactic collimator is removed and thereafter a radiographic image thereof must be acquired under a wide radioscopic region.